Lithium batteries are widely used in consumer electronics due to their relatively high energy density. Rechargeable batteries are also referred to as secondary batteries, and lithium ion secondary batteries generally have a negative electrode material that incorporates lithium when the battery is charged. For some current commercial batteries, the negative electrode material can be graphite, and the positive electrode material can comprise lithium cobalt oxide (LiCoO2). In practice, only a modest fraction of the theoretical capacity of the positive electrode active material generally can be used. At least two other lithium-based positive electrode active materials are also currently in commercial use. These two materials are LiMn2O4, having a spinel structure, and LiFePO4, having an olivine structure. These other materials have not provided any significant improvements in energy density.
Lithium based batteries are generally classified into two categories based on their application. The first category involves high power battery, whereby lithium based battery cells are designed to deliver high current (Amperes) for such applications as power tools and Hybrid Electric Vehicles (HEVs). However, by design, these battery cells are lower in energy since a design providing for high current generally reduces total energy that can be delivered from the battery. The second design category involves high energy batteries, whereby lithium based battery cells are designed to deliver low to moderate current (Amperes) for such applications as cellular phones, lap-top computers, Electric Vehicles (EVs) and Plug in Hybrid Electric Vehicles (PHEVs) with the delivery of higher total capacity.
Electrolytes provide for ionic conductivity through the batteries between the cathodes and anodes. For most commercial batteries, a liquid electrolyte is used. The properties of the electrolyte can influence significantly the battery performance. For outdoor use, such as for vehicles, the batteries are subjected to conditions spanning over a wide temperature range. It is also desirable for the batteries to operate over a large number of charge-discharge cycles so that the batteries can provide a larger economic value.